In the manufacturing of vitreous bonded CBN tool the porosity change associated with various processing conditions, I. e. the sintering temperature and the size and the amount of abrasive grits was observed. In the case of sintering of vitreous bond material only the specimen density reached the maximum at 950$^{circ}C$ and then the total porosity was increased slightly with the temperature above 950$^{circ}C$. In the sintering of a-brasive grits and the vitreous bond material together a marked increase in the total porosity was found with the temperature above 950$^{circ}C$ Reducing the grit size at the constant volume fraction of abrasive grits showed an increase in the total porosity at whole sintering temperature. On the contrary. it was observed that increasing the volume fraction of abrasive grits with a same size showed the increased open porosity simultaneously with decreased closed porosity at whole sintering temperature.